bill Shurvinton

I've got a Sportsman XL on order plus an additional resonator if I need more for track days. Exhaust options are a little limited on my car (Lotus 7 clone) as it is a side exhaust design, unless I go to very short primaries, in which case I can add a second box.

I bought the spintech mainly to be different and because I was fed up trying to get a steel packed one to work. What will be interesting is seeing the effect it has on the tuning. I haven't seen anything published on the effects of the reflections from the muffler on the overall system tuning in a rotary, but I always worry about the racing beat long primary system as it has a muffler in each primary, but at different points. These mufflers will produce a reflection, so the 2 rotors will be tuned for different RPM.

Bill

rotarygod

iTrader: (1)

I used to have the Racing Beat long primary system but recently sold it. There are a couple of very big flaws with the system. The first one is that the main pipes are 2" diameter. This isn't where the problem lies though. The collector on this system is immediately before the muffler and is part of the muffler assembly. The problem is that the 2 pipes on the muffler immediately before collecting are only 1 3/4" not 2". This leaves a big lip in the exhaust path. The decrease in area also isn't good for power. It does collect nicely into a 2 1/2" pipe though. To make matters worse in this location is that the gasket that comes with it is even smaller still, further restricting flow. I had to go through with a die grinder and enlarge the gasket as well as the pipe openings up to 2". This helped get rid of turbulence but still couldn't help the decrease in cross sectional area. The second big problem my system had was with the back pressure sensing tube on one of the pre-silencers. This system can be purchased with or without this tube but it is necessary to activate the 6 port system on the GSL-SE. This tube protrudes into the airstream and then makes a 90 degree turn to face upstream. The total diameter of this tube is about 3/4" of an inch. Its total area subtracted from the area of the pipe causes a very noticable restriction on only 1 rotor. You can also hear the exhaust rushing past this tube so it sounds like an exhaust leak if you don't know what you are listening to. Regardless of these problems it still made more power than any other system that I have had on the car to date. However I will rememdy that situation very soon. The exhaust also did not fit the car very well, hitting heat shields and not lining up with hangers. In my opinion, the Racing Beat system with its flaws and 75 lb. weight penalty is not worth even half of what it is priced at new. It gives good power but is very poorly designed and engineered. More power could have been had from this system for only a few more dollars spent on engineering. This is where I feel the system lacks the most; engineering. They knew that a certain length exhaust would work wonderful but then they took shortcuts to sell the system with currently available parts like the early RX-7 dual inlet mufflers. For half the price I can design and build a lighter, and more powerful system. Everyone swears by Racing Beat as gods and yes they are very knowledgeable and have done some wonderful things for the rotary community but some of their products are overpriced and underengineered. This is at least true when it comes to their exhausts. Like I said earlier, brand name means nothing if the part is low quality. This was a very good example.

bill Shurvinton

Never seen a racing beat system up close, so can't comment on that aspect. Do know that the mufflers are too heavy and expensive for my app. (1300lb car needs light everything)

Come the fall I should have bedded in and tuned the car enough that I will be ready to experiment with tuned lengths a bit more

RETed

I am totally against high overlap rotary motors.&nbsp I've heard all the arguments for the overlap, and references are still being made to piston engines.&nbsp I believe the comparison is not valid.

Most modern day piston engines with multi valves and cross flow heads can use overlap to draw the intake charge into the combustion chamber.&nbsp If we use that theory and apply it to a rotary engine, the intake charge goes into the intake passages and takes a dive into the direction of the exhaust port - this is detrimental to attaining proper velocity vectors in the same direction of the spinning rotor and eventually in the "combustion chamber" fronting the spark plug locations.&nbsp Now, it takes some pretty complex mathematics and computer modeling to get a good idea of proper overlap values are advantageous, but I think claiming "more is better" thinking in overlap is pure BS.

I think the reason "race" engines run BP's, JB's, and PP's is just to increase VE because the stock port size is the restriction at those high RPM's.&nbsp Look at their induction systems -very short runners going into the engine.

Overlap is something unavoidable when "porting" the rotary engine.



-Ted

bill Shurvinton

You've lost me. I've just gone through the thread again to find where high overlap was introduced and can't. Please elucidate

Bill

rotarygod

iTrader: (1)

Yeah I guess I can see that. Too bad the engines start with a small amount of overlap. The Renesis has 64 degrees of dwell yet makes tons more power. Gets you wondering doesn't it.

bill Shurvinton

Re: renesis extra HP is it that surprising?

12% comes from higher redline, with no torque increase required.

The side port exhaust one can assume is quieter than the PP type if inlet is anything to go by, so doesn't need the rapid expansion of older designs. Therefore it will flow better in a noise friendly configuration (aside: of the few technical reports on the side port I have seen, the main advantage that has been touted is Nox reduction)

The renesis uses tuned inlet and exhaust lengths. IIRC there are 3 lengths for each, so they can tune the engine for better operation at high RPM without sacrificing low end.

230HP in a NA 13B has been readily possible for some time with good street ports, but only with compromises lower down in the band and/or lots of noise.

I guess the proof of the pudding will be when someone gets a renesis and starts playing with the porting to get more power.

Meantime I need to get back to some sums

RETed

There was a small reference made by rotarygod:



-Ted

RETed

If you're trying to imply more overlap makes more power, that's a very bad assumption.



-Ted

banzaitoyota

I too have a spintech, haven't completed the system yet...as always

bill Shurvinton

Ah, Missed that in my scan. Sorry.

Did get to read through those Cafe articles this evening. Whether you believe that scavenging is beneficial or not (or even if you subscribe to a BP turbo being a variant on the miller cycle) there is a nice refresher/introduction to exhaust tuning in there, and the EPG plots show really nicely where the trade-offs are when tuning. Of course the aircraft boys have it easy as they are optimising for a very narrow RPM band and can spend time opening the throttle and leaning the mixture.

I need to go and digest.

rotarygod

iTrader: (1)

Ted: I way agreeing with your comment.

bill Shurvinton

Did some quick sums last night, at least enought to give me a starting point for when I get around to getting a new exhaust made up. I also realised that, where you cannot fit the tuned length you want in, that you can adjust the ID of the tube a little, which will change the flow rate and therefore the tuned length.

I may put some ports on to allow pressure logging just to see what it looks like. Either that or just buy a load of bits and some dyno time which is usually quicker.

I need to find more on megaphone theory and how glass packs act. Effectively a glass pack looks like a megaphone to the exhaust flow, so this could be used beneficially in the design.

For real esoterica you could consider the systems that MSD sell for 2 strokes where you inject water to increase the density of the exhaust gas and change the tuning.

Bill

Makenzie71

wow...5 stars...my first "star worthy" thread...I'm touched.

Thanks for all of the info guys...please, all is welcome.

rxspeed87

ok with the backpressure I disagree with it being needed

backpressure is resistance to flow.
the more resistance the less your exhuast can flow
and when you put a resistance to flow in there it slows the exhuast down

an ideal exhuast would be a vacuume. but that sure as hell isn't going to happen

and with a large exhuast in a way it is almost as though it has backpressure in itself
only thing is the backpressure isn't comming from the walls or anything else
it is the exhuast gas themselves that makes the restriction.


backpressure however you look at it is the devil


the rest of it for the most part seemed ok
kinda just skimmed it

drago86

Megaphones broaden the rpm band in which the "tune" in the exaust happens, the gradual increase in diameter gradually reflects back the pressure waves, the net effect is a slightly less strong effect over a slightly wider rpm band, also backpressure naturally does the water injection thing to an extent, which is why you see stingers on 2 strokes. A glasspack would increase in diamete fairly quickly, so it would have a very small megaphone effect.

bill Shurvinton

Not sure I agree on the glasspack front as if you pack them more densely the wave diffusion will decrease. Needs some testing though.


I know 'what' megaphones and stingers do, I need to spendmore time analysing the 'how' wrt a rotary. it requires you to start with accepting a high overlap timing and then optimising the scavenging effects to make the most of it. it's one of those areas of study that could end up as self defeating, but I need to redesign my exhaust system anyway, so might as well experiment.

Bill

Makenzie71

hmmm...I thought this thread would survive longer...

Wankels-Revenge

Good god this thread is great. Has it been stickied yet...or archived or something? If not can i ask that someone do so? A thread like this is gold.

honegod

I am wondering if there is a limit to the effective length of a glasspack style muffler, as in would two glasspacks in a row muffle twice as much as just one, and would four muffle twice as well as two ?

if so, why not build the entire system out of glasspacks ?
{aside from lifespan problems }

also, if glasspacks look like a megaphone, wouldn't a full glasspack system act like a megaphone of whatever length the pipes end up being with an outlet diameter of an impressive dimension ?

might having twin megaphones 6' long with a 2' outlet diameter {virtual} work well enough that collecting the two pipes might not be needed ?

I am thinking about broad powerband applications rather than peak horsepower, and street quiet

RETed

Who the hell dug this one back up from the grave!


-Ted

Makenzie71

bumped for fear of deletion...

Makenzie71

Sorry it's three months late for response but for future reference...

I kinna got lost in reading that as to what your wanting to build your exhaust from but I'm going with the first easily definable route...an exhaust constructed entirely of glasspacks.

Soundwaves travel in all directions from it's source. Sound is carried through the atmosphere by the colision of molecules of air or whatever with one another until they reach an obstruction. Then they reflect away from this obstruction. If you let a single drop of water fall into a bowl you'll see the ripples all travel away from the point of impact and reflect off the walls and back and such. Same principal.

In order for the sound to deaden air must travel away from teh source with the sound. Don't really know yet if any of that was relevent to my explanation but I'm tired and drinking so bear with me.

Anyways, when your exhaust gasses flow into a glass pack (straight through and baffle-less) the gasses must expand into the packing. This means that the same amount of gasses flowing through a 2.5" pipe must now expand to pressurize a 6" diameter pipe. The packing takes up some of this volume but still, the gas must expand, and when the gasses expand they lose momentum. This loss of constant pressure effects both my scavenging theories and Rotarygod's similar...yet somehow very different...explanations.

An exhaust created entirely of glasspacks will suffer from this, only instead of a 12" section at the rear it'll suffer through the entire system. With the gasses constantly having to expand to pressurize the tubing you leave zero backpressure and lots of resistance.

tannji

OK, 6 months later, can any of the people who bought the spintech systems comment on their performance and sound? Especially sound.... they seem to be proven to perform.... but I am looking for less sound, and less of a "rice" sound as well, easily the aspect of the rotary I least like. I appreciate the sounds of crotch rockets and gas power RC aircraft.... from a distance, I would like to avoid having a car apparently powered by a bike/RC plane combo.

tannji

tannji

Also, would any of the "elucidators" care to post on theory and application of X-pipes and H-pipes? and on performance and sound with a pre-silencer? As I said before, looking for the best ratio between sound and performance.

tannji